1. Field of Invention
The present invention relates to a decoding device, an encoding device, an interpolation frame creating system, an integrated circuit device, a decoding program and an encoding program, particularly to a decoding device, an encoding device, an interpolation frame creating system, an integrated circuit device, a decoding program and an encoding program for creating interpolation frames.
2. Description of the Related Art
For TVs, personal computers (PCs), cellular phones, and other types of apparatus displaying image signals, a technique for creating interpolation frames which interpolate image frames forming an image signal and displaying the created interpolation frames being inserted between the image frames is known. This technique is utilized for two different purposes: to display an image signal transmitted at a low frame rate to look smooth; and to encode and transmit an image signal at a low bit rate.
As one of the techniques intended for the former purpose, a technique to detect a motion vector between image frames and to create an interpolation frame using the obtained motion vector is known (see, for example, Japanese Laid-Open Publication No. 7-177514, FIG. 5).
More specifically, a motion vector between the image frames is detected, and the detected motion vector is divided internally or externally in the ratio between a distance in terms of time between the image frames and a distance in terms of time to an interpolation position of the interpolation frame. The derived motion vector (hereinafter, referred to as an interpolation motion vector) and pixel values of the image frames are used to create an interpolation frame.
A technique of transmitting pixel values of an image signal which correspond to an interpolation frame for a portion where a precision of interpolation using an interpolation motion vector is low in order to improve the precision of the interpolation frame is also known (see, for example, Japanese Patent Gazette No. 2828096).
As one of the techniques intended for the latter purpose, a technique called motion compensation encoding is known. Motion compensation encoding is encoding performed using motion vectors of image blocks which form an image frame. For example, in Moving Picture Experts Group (MPEG), which is an international standard for compression of moving picture signals, two encoding methods of intra-coding and inter-coding are used. Intra-coding is a method for encoding an image frame with only information within that frame. An image frame encoded with this method is called I frame. Inter-coding is a method for encoding an image frame using both information within that frame and information of other frames. An image frame encoded with this method is called P frame or B frame.
Specifically, motion compensation encoding intended for the latter purpose is a technique of encoding motion vectors between an interpolation frame (B frame) and image frames (I frames or P frames) which are positioned bidirectionally with respect to the interpolation frame in terms of time, and residual information of the interpolation frame and the image frames which are compensated with the motion vectors, as information for creating an interpolation frame. On a decoding end, an encoded image signal and image frames which have already been decoded are used to create an interpolation frame.
In this technical field, there is a demand for creating interpolation frames with a high precision while further improving encoding efficiency. Specifically, among the two techniques described above, it is desired to create interpolation frames with a higher precision in the former technique, and it is desired to improve the encoding efficiency in the latter technique.
An object of the present invention is to provide a decoding device, an encoding device, an interpolation frame creating system, an integrated circuit device, a decoding program and an encoding program for creating interpolation frames with a high precision while improving encoding efficiency.